Emergency "Bad Boy" ultra Compact charger

[Doctorbass]

"Bad boy charger"

I plan to work on a very light weight emergency charger, to transport with my ebike in case where my pack would go empty faster than i would have expected.


I often heard about a "bad boy charger" that only use few component like a dimmer and a 1:1 transfo with sec and primary serie linked to increase voltage for EV that need more than 169V wich is the peak volt of a 120V RMS outlet. For sure, i know that with this type of charger, the battery pack and the rest of the electrical system of the ebike WOULD NOT BE ISOLATED FROM THE AC LINE and would need special care to avoid electrical shock! :lol:

I just wonder if with few capacitor calculated with 60Hz or a simple light dimer that use a triac combined with a coil and a diode in serie i could finally acheived to a light charger that could give 10-15A at for exemple 84V DC

I dont talk about resistor.. that would dissipate the differential voltage into heat!...

for details see exemple of Bad boy charger: http://www.evalbum.com/tech/


...And of course, it would be used to "add" some Ah to the pakc.. not to fully charge it!... and would need to watch continuously the charging process and the SOC.


any crazy idea?

Doc

 

[fechter]

Yikes! that's pretty scarey.

At least put a FUSE in the line somewhere! One fuse on each line would be better.

It would be good to measure the current also. A small analog ammeter would be nice.

Using a triac, the peak current will be much higher than the average.

 

[lawsonuw]

How about adding a Plug-in GFCI to the end of the power cord? Also, http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=102-1338-ND is pretty cheap, and since it's isolated the outputs of two could be put in series. Looks like 91V is about as low as a pair would go without hacking.

Marty

 

[shredator]

I was thinking about doing almost the same thing. Would you need any filtering at all? or is there some reason that the cells or bms cant handle the noise from the rectifier or dimmer switch?
something like this would work well for me because there is an outdoor outlet that is right by the bike rack at my work.
perhaps the issue with the bike not being isolated from the ac mains could work to your advantage as a theft deterrent :wink:

 

[monster]

my emergency bad boy charger melted today and almost caught fire

 

[monster]

here is the ultimate bad boy charger
or the killa-charger as i like to call it


its about 80% efficient yet it still gives off enough heat to melt heat shrink on batteries

 

[monster]

in a light weight portable "bad boy" charger any transformers defeat the point because they are either heavy or limit the current.

 

[lazarus2405]

I'm really interested in this idea here. Since I run a pretty high pack voltage, I figure it should pretty easy to make a Bad Boy. So, my goal is a charger that would be compact and easy to carry, that could charge my pack from dead to full in an hour, that I could use to top off the pack when out and about.

This here really caught my eye:

http://www.evalbum.com/tech/bonn_charger.html

:lol:

So, if my pack is 112v nominal and I know that I can safely charge it at at least ~10a (perhaps as much as 3x that... fast charging info on emolis is conflicting), and I want to charge it off 115vAC mains, what do I need?

Here's what I'm thinking:

GFCI - where can i get a compact one?
12a 120vAC breaker - again, compactness?
Bridge rectifier - I have a pair of GBPC3504 units. Is one suitable?
little analog ammeters and voltmeters for monitoring - easy to find
filter caps - will I need any, and how much of what sorts?

And the hard part - changing the voltage. I just measured the bridge rectifier, and from a 115vAC socket I'm getting 104vDC out of it. Bleh. I want to charge the pack at 114v-115v, so what's the easiest way to achieve this?

And charging current: without a current-limiting power supply, the charging current to the batteries will be dependent upon the charging voltage, the pack voltage, the pack resistance, and Ohm's law, correct? And to safely charge the pack, I need to know my internal resistance, correct?

And is measuring my pack's internal resistance as simple as measuring the voltage sag at a known current?

 

[safe]

How many DC volts?

If you do something basic like a bridge rectifier and a capacitor how many DC volts would you get from a standard AC plug? (120 VAC)

104vDC? (see above)

I wonder if you could do this with a timer and if you were careful about watching and knowing what you are doing if you could survive with this for something like SLA or NiMh?

Seems that the main problem is stepping the voltage from 104 volts down to whatever you are using... :?

It makes one think that one ought to design the bikes battery around the wall socket... make the bikes voltage be a direct match for common AC power. (after stepping down to DC) Then you could do the DC-to-DC step down on the bike to deliver the power or just standardize EVERYTHING around a single voltage.

 

[fechter]

How many DC volts?

If you do something basic like a bridge rectifier and a capacitor how many DC volts would you get from a standard AC plug? (120 VAC)

Actually, you get around 165 volts. The capacitor will charge to the peak of the AC waveform.

 

[lazarus2405]

Seems that the main problem is stepping the voltage from 104 volts down to whatever you are using... :?

From what I understand, the easiest way would be a variac before the rectifier. Hence the light dimmer.

So, will a standard light dimmer increase the voltage? Something with a 120%-50% range would be perfect, I think.

So, what exactly is the purpose of the capacitor? Just filter? What are the requirements on it?

And what would the purpose of a triac thrown into all this be?

 

[monster]

are variac's and light dimmers the same thing? i have a big variac but i don't know how to make it into a charger. i think it would only be good for a trickle charge right?

 

[Link]

are variac's and light dimmers the same thing?

No. Variacs are basically a transformer with loads of taps on it. A light dimmer uses a triac and a capacitor to clip off the AC waveform of mains power.

 

[monster]

so does it get hot?

 

[lazarus2405]

A light dimmer uses a triac and a capacitor to clip off the AC waveform of mains power.

Oh. I thought they used variacs.

But yeah, a variac is to a transformer as a potentiometer is to a resistor. A transformer that can be varied between a range of values.

So I need someone who knows their stuff to help out. Can I use a variac and a bridge rectifier to get an adjustable voltage of 120VDC-80VDC and 10 amps from a 115VAC outlet? What else do I need in the circuit (other than and AC breaker, a DC fuse, and a GFCI)? And how do I control the current?

 

[fechter]

A variac and a bridge rectifier will work great. The EV car guys use them frequently. Only problem is the current rating on the variac has to be observed. A 2 amp unit is pretty heavy. A 10 amp unit is extremely heavy. The filter capacitor is probably unnecessary.

A triac light dimmer would be much lighter, but will have very high current peaks. You can vary the average current, but the peak will be the same as a direct connected line. Perhaps some kind of 'ballast' would level out the peaks. A ballast is usually a large inductor, but in this case, perhaps a large series capacitor might work. Something like an AC induction motor starter capacitor.

 

[safe]

A variac and a bridge rectifier will work great.

Hmmmmm....

This is all very interesting.

For a low budget "bad boy charger" you could have:

Light Dimmer (to adjust the total power) $5

Bridge Rectifier (to convert to DC) $5

Large Capacitor (to smooth the DC) $5

Max 60 minute Timer (to limit the charge) $10

...after some fiddling around to get things right you would "know" what to expect and you could have a very fast charge system for very little money.

I think the idea might be to divide your pack into smaller units (so a 48 volt pack might be broken down into four 24 volt units, 2 series, 2 parallel) and then use the Light Dimmers on each one. That way the amps going through each one is less of a problem. Either that or just buy a more expensive Light Dimmer.

But did you say that the Dimmer is only going to limit the current and not effect voltage? (which is a sickening 165 volts)

That means that voltage regulation needs to happen somehow...

It seems to me that it would be easier to just buy one of these:

$18 - 36V @ 4.2A 150W POWERSUPPLY1 POWER SUPPLY

http://www.powersupplydepot.com/productview.asp?product=13657+PS

They have various voltages that you could get for you own needs... so you could shop a little...

 

[EMF]

He wants 10 - 15 amps at 84 volts If you read the thread...

 

[safe]

He wants 10 - 15 amps at 84 volts If you read the thread...

My point was that if (as Fechter says) you start with 165 DC volts you need to take that down to something you can work with. The Light Dimmer is able to lower the current, but not neccessarily the voltage.

I'm just pointing out that it's the voltage regulation step that seems to be missing here. You might be better off designing the pack to suit the voltage (165v) rather than change the voltage to suit the pack.

 

[lazarus2405]

He wants 10 - 15 amps at 84 volts If you read the thread...

My point was that if (as Fechter says) you start with 165 DC volts you need to take that down to something you can work with. The Light Dimmer is able to lower the current, but not neccessarily the voltage.

I'm just pointing out that it's the voltage regulation step that seems to be missing here. You might be better off designing the pack to suit the voltage (165v) rather than change the voltage to suit the pack.

A transformer might be appropriate. Again, though, I don't know how big it would have to be to carry 10a, but it might be a heck of a lot smaller than a variac.

Fechter, we really need for you to hold our hands here. Safe and I are really throwing sticks at shadows and hoping to catch a meal. :|

 

[EMF]

He wants 10 - 15 amps at 84 volts If you read the thread...

My point was that if (as Fechter says) you start with 165 DC volts you need to take that down to something you can work with. The Light Dimmer is able to lower the current, but not neccessarily the voltage.

I'm just pointing out that it's the voltage regulation step that seems to be missing here. You might be better off designing the pack to suit the voltage (165v) rather than change the voltage to suit the pack.

My point is, that when I looked at power supplies for my ebike on ebay, once you start looking at high voltage and high amps, those things get expensive! Maybe this is a goal or idea behind the Bad Boy charger that DrBass is talking about. A cheap quick and dirty charge solution. I don't know..

 

[safe]

....those things get expensive! Maybe this is a goal or idea behind the Bad Boy charger that DrBass is talking about. A cheap quick and dirty charge solution.

Now you're getting it... the idea is to find "less than ideal" but cheap ways to throw energy into your battery. It ain't pretty, but it gets the job done. (just don't fret too much about an imperfect charge... these ideas tend to require that perfection is ignored)

That's why it's a "bad boy" concept... it's a little "dirty"... :lol:

 

[EMF]

Thanks for the news flash - I'm getting it? I got it from the first post. I think you are suffering from lead poisoning.

 

[fechter]

A switching mode power supply is the "normal" way to do it. Also big, heavy, expensive...

The idea is to make a charger with NO transformer. A 60hz transformer of any kind will make the thing very heavy and defeat the purpose of the exercise. You might as well just carry a normal charger.

You don't regulate the voltage with the "Bad Boy". You're supposed to watch the voltage manually and terminate the charge when it gets too high. This could be automated I suppose.

An triac based light dimmer is really a switch that is either on or off. It just switches at 120hz. By reducing the duty cycle, the average current will be reduced, but the peak current will be a function of the peak voltage and the circuit (mostly battery) resistance.

If the light dimmer is always turning on during the last half of the cycle, then you could control the peak voltage (and therefore the current). If the dimmer turns on anywhere in the first half of the cycle, it will stay on through the rest of the cycle, including the peak.

Perhaps a light dimmer with a restricted control pot might work

 

[Doctorbass]

A switching mode power supply is the "normal" way to do it. Also big, heavy, expensive...

The idea is to make a charger with NO transformer. A 60hz transformer of any kind will make the thing very heavy and defeat the purpose of the exercise. You might as well just carry a normal charger.

You don't regulate the voltage with the "Bad Boy". You're supposed to watch the voltage manually and terminate the charge when it gets too high. This could be automated I suppose.

An triac based light dimmer is really a switch that is either on or off. It just switches at 120hz. By reducing the duty cycle, the average current will be reduced, but the peak current will be a function of the peak voltage and the circuit (mostly battery) resistance.

If the light dimmer is always turning on during the last half of the cycle, then you could control the peak voltage (and therefore the current). If the dimmer turns on anywhere in the first half of the cycle, it will stay on through the rest of the cycle, including the peak.

Perhaps a light dimmer with a restricted control pot might work

That's the exact goal of this charger type.

I just wonder if adding an inductor at the outout of the triac would smooth the HF and decrease the peak volt.. helping to lower it but keeping the same mean voltage over a complete cycle?

so a dimmer with combined inductor in serie and a caps paralleled to the output of that... (a LC low pass circuit ).. smaller than a transformer efficient...